Effect of temperature on the hydrodynamics of a fluidized bed circulating in a long tube for a solar energy harvesting application

Abstract

The particle-in-tube solar receiver concept for solar towers uses fluidized particles as heat transfer fluids. The experiments are conducted with a single tube of aspect ratio H/D = 67 irradiated over a 1-m height using concentrated solar energy. Olivine particles of Geldart’s Group A are used. Fluidization regimes are identified thanks to pressure signal analyses, and regime maps are plotted depending on the temperature in the range 150–700 °C. Both the local slip Reynolds number and the particle temperature govern the regime transitions. The limits and size of the turbulent fluidization regime domain decrease with temperature. The particle volume fraction also decreases with temperature. Finally, the intensity of the wall-to-particle heat transfer is discussed as a function of the fluidization regimes. As an indicator of the heat transfer intensity, a dimensionless coefficient is derived. This coefficient increases with temperature and exhibits the highest values for the turbulent fluidization regime.